3 files changed, 5 insertions, 3 deletions
diff --git a/src/dotty/tools/dotc/core/ConstraintHandling.scala b/src/dotty/tools/dotc/core/ConstraintHandling.scala
index 6371a176b..02f5bf87f 100644
--- a/src/dotty/tools/dotc/core/ConstraintHandling.scala
+++ b/src/dotty/tools/dotc/core/ConstraintHandling.scala
@@ -35,7 +35,7 @@ trait ConstraintHandling {
   
   implicit val ctx: Context
   
-  def isSubType(tp1: Type, tp2: Type): Boolean
+  protected def isSubType(tp1: Type, tp2: Type): Boolean
   
   val state: TyperState
   import state.constraint
diff --git a/src/dotty/tools/dotc/core/Skolemization.scala b/src/dotty/tools/dotc/core/Skolemization.scala
index 2e517c90e..8bc5c815f 100644
--- a/src/dotty/tools/dotc/core/Skolemization.scala
+++ b/src/dotty/tools/dotc/core/Skolemization.scala
@@ -7,6 +7,8 @@ import collection.mutable
 /** Methods to add and remove skolemtypes.
  *  
  *  Skolem types are generated when comparing refinements. 
+ *  A skolem type is simply a fresh singleton type that has a given type
+ *  as underlying type.
  *  Two skolem types are equal if they refer to the same underlying type. 
  *  To avoid unsoundness, skolem types have to be kept strictly local to the
  *  comparison, they are not allowed to escape the lifetime of a comparison
diff --git a/src/dotty/tools/dotc/core/TypeComparer.scala b/src/dotty/tools/dotc/core/TypeComparer.scala
index 1de2d7e98..db6e504d5 100644
--- a/src/dotty/tools/dotc/core/TypeComparer.scala
+++ b/src/dotty/tools/dotc/core/TypeComparer.scala
@@ -88,7 +88,7 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling wi
         assert(isSatisfiable, constraint.show)
   }
 
-  def isSubType(tp1: Type, tp2: Type): Boolean = ctx.traceIndented(s"isSubType ${traceInfo(tp1, tp2)}", subtyping) /*<|<*/ {
+  protected def isSubType(tp1: Type, tp2: Type): Boolean = ctx.traceIndented(s"isSubType ${traceInfo(tp1, tp2)}", subtyping) /*<|<*/ {
     if (tp2 eq NoType) false
     else if (tp1 eq tp2) true
     else {
@@ -179,7 +179,7 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling wi
             else
               (tp1.name eq tp2.name) &&
               isSameType(tp1.prefix, tp2.prefix) &&
-              (tp1.signature == tp1.signature) &&
+              (tp1.signature == tp2.signature) &&
               !tp1.isInstanceOf[WithFixedSym] &&
               !tp2.isInstanceOf[WithFixedSym]
             ) ||