diff --git a/internal/typeparams/coretype.go b/internal/typeparams/coretype.go
new file mode 100644
index 0000000..993135e
--- /dev/null
+++ b/internal/typeparams/coretype.go
@@ -0,0 +1,122 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package typeparams
+
+import (
+	"go/types"
+)
+
+// CoreType returns the core type of T or nil if T does not have a core type.
+//
+// See https://go.dev/ref/spec#Core_types for the definition of a core type.
+func CoreType(T types.Type) types.Type {
+	U := T.Underlying()
+	if _, ok := U.(*types.Interface); !ok {
+		return U // for non-interface types,
+	}
+
+	terms, err := _NormalTerms(U)
+	if len(terms) == 0 || err != nil {
+		// len(terms) -> empty type set of interface.
+		// err != nil => U is invalid, exceeds complexity bounds, or has an empty type set.
+		return nil // no core type.
+	}
+
+	U = terms[0].Type().Underlying()
+	var identical int // i in [0,identical) => Identical(U, terms[i].Type().Underlying())
+	for identical = 1; identical < len(terms); identical++ {
+		if !types.Identical(U, terms[identical].Type().Underlying()) {
+			break
+		}
+	}
+
+	if identical == len(terms) {
+		// https://go.dev/ref/spec#Core_types
+		// "There is a single type U which is the underlying type of all types in the type set of T"
+		return U
+	}
+	ch, ok := U.(*types.Chan)
+	if !ok {
+		return nil // no core type as identical < len(terms) and U is not a channel.
+	}
+	// https://go.dev/ref/spec#Core_types
+	// "the type chan E if T contains only bidirectional channels, or the type chan<- E or
+	// <-chan E depending on the direction of the directional channels present."
+	for chans := identical; chans < len(terms); chans++ {
+		curr, ok := terms[chans].Type().Underlying().(*types.Chan)
+		if !ok {
+			return nil
+		}
+		if !types.Identical(ch.Elem(), curr.Elem()) {
+			return nil // channel elements are not identical.
+		}
+		if ch.Dir() == types.SendRecv {
+			// ch is bidirectional. We can safely always use curr's direction.
+			ch = curr
+		} else if curr.Dir() != types.SendRecv && ch.Dir() != curr.Dir() {
+			// ch and curr are not bidirectional and not the same direction.
+			return nil
+		}
+	}
+	return ch
+}
+
+// _NormalTerms returns a slice of terms representing the normalized structural
+// type restrictions of a type, if any.
+//
+// For all types other than *types.TypeParam, *types.Interface, and
+// *types.Union, this is just a single term with Tilde() == false and
+// Type() == typ. For *types.TypeParam, *types.Interface, and *types.Union, see
+// below.
+//
+// Structural type restrictions of a type parameter are created via
+// non-interface types embedded in its constraint interface (directly, or via a
+// chain of interface embeddings). For example, in the declaration type
+// T[P interface{~int; m()}] int the structural restriction of the type
+// parameter P is ~int.
+//
+// With interface embedding and unions, the specification of structural type
+// restrictions may be arbitrarily complex. For example, consider the
+// following:
+//
+//  type A interface{ ~string|~[]byte }
+//
+//  type B interface{ int|string }
+//
+//  type C interface { ~string|~int }
+//
+//  type T[P interface{ A|B; C }] int
+//
+// In this example, the structural type restriction of P is ~string|int: A|B
+// expands to ~string|~[]byte|int|string, which reduces to ~string|~[]byte|int,
+// which when intersected with C (~string|~int) yields ~string|int.
+//
+// _NormalTerms computes these expansions and reductions, producing a
+// "normalized" form of the embeddings. A structural restriction is normalized
+// if it is a single union containing no interface terms, and is minimal in the
+// sense that removing any term changes the set of types satisfying the
+// constraint. It is left as a proof for the reader that, modulo sorting, there
+// is exactly one such normalized form.
+//
+// Because the minimal representation always takes this form, _NormalTerms
+// returns a slice of tilde terms corresponding to the terms of the union in
+// the normalized structural restriction. An error is returned if the type is
+// invalid, exceeds complexity bounds, or has an empty type set. In the latter
+// case, _NormalTerms returns ErrEmptyTypeSet.
+//
+// _NormalTerms makes no guarantees about the order of terms, except that it
+// is deterministic.
+func _NormalTerms(typ types.Type) ([]*Term, error) {
+	switch typ := typ.(type) {
+	case *TypeParam:
+		return StructuralTerms(typ)
+	case *Union:
+		return UnionTermSet(typ)
+	case *types.Interface:
+		return InterfaceTermSet(typ)
+	default:
+		return []*Term{NewTerm(false, typ)}, nil
+	}
+}
diff --git a/internal/typeparams/coretype_test.go b/internal/typeparams/coretype_test.go
new file mode 100644
index 0000000..2884399
--- /dev/null
+++ b/internal/typeparams/coretype_test.go
@@ -0,0 +1,105 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package typeparams_test
+
+import (
+	"go/ast"
+	"go/parser"
+	"go/token"
+	"go/types"
+	"testing"
+
+	"golang.org/x/tools/internal/typeparams"
+)
+
+func TestCoreType(t *testing.T) {
+	if !typeparams.Enabled {
+		t.Skip("TestCoreType requires type parameters.")
+	}
+
+	const source = `
+	package P
+
+	type Named int
+
+	type A any
+	type B interface{~int}
+	type C interface{int}
+	type D interface{Named}
+	type E interface{~int|interface{Named}}
+	type F interface{~int|~float32}
+	type G interface{chan int|interface{chan int}}
+	type H interface{chan int|chan float32}
+	type I interface{chan<- int|chan int}
+	type J interface{chan int|chan<- int}
+	type K interface{<-chan int|chan int}
+	type L interface{chan int|<-chan int}
+	type M interface{chan int|chan Named}
+	type N interface{<-chan int|chan<- int}
+	type O interface{chan int|bool}
+	type P struct{ Named }
+	type Q interface{ Foo() }
+	type R interface{ Foo() ; Named }
+	type S interface{ Foo() ; ~int }
+
+	type T interface{chan int|interface{chan int}|<-chan int}
+`
+
+	fset := token.NewFileSet()
+	f, err := parser.ParseFile(fset, "hello.go", source, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var conf types.Config
+	pkg, err := conf.Check("P", fset, []*ast.File{f}, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	for _, test := range []struct {
+		expr string // type expression of Named type
+		want string // expected core type (or "<nil>" if none)
+	}{
+		{"Named", "int"},         // Underlying type is not interface.
+		{"A", "<nil>"},           // Interface has no terms.
+		{"B", "int"},             // Tilde term.
+		{"C", "int"},             // Non-tilde term.
+		{"D", "int"},             // Named term.
+		{"E", "int"},             // Identical underlying types.
+		{"F", "<nil>"},           // Differing underlying types.
+		{"G", "chan int"},        // Identical Element types.
+		{"H", "<nil>"},           // Element type int has differing underlying type to float32.
+		{"I", "chan<- int"},      // SendRecv followed by SendOnly
+		{"J", "chan<- int"},      // SendOnly followed by SendRecv
+		{"K", "<-chan int"},      // RecvOnly followed by SendRecv
+		{"L", "<-chan int"},      // SendRecv followed by RecvOnly
+		{"M", "<nil>"},           // Element type int is not *identical* to Named.
+		{"N", "<nil>"},           // Differing channel directions
+		{"O", "<nil>"},           // A channel followed by a non-channel.
+		{"P", "struct{P.Named}"}, // Embedded type.
+		{"Q", "<nil>"},           // interface type with no terms and functions
+		{"R", "int"},             // interface type with both terms and functions.
+		{"S", "int"},             // interface type with a tilde term
+		{"T", "<-chan int"},      // Prefix of 2 terms that are identical before switching to channel.
+	} {
+		// Eval() expr for its type.
+		tv, err := types.Eval(fset, pkg, 0, test.expr)
+		if err != nil {
+			t.Fatalf("Eval(%s) failed: %v", test.expr, err)
+		}
+
+		ct := typeparams.CoreType(tv.Type)
+		var got string
+		if ct == nil {
+			got = "<nil>"
+		} else {
+			got = ct.String()
+		}
+		if got != test.want {
+			t.Errorf("coreType(%s) = %v, want %v", test.expr, got, test.want)
+		}
+	}
+}