Tweaks in wording of error messages

Author: odersky

compiler/src/dotty/tools/dotc/core/TypeComparer.scala

@@ -2591,8 +2591,8 @@ object TypeComparer {
       def addLow: Repr = approx | LoApprox
       def addHigh: Repr = approx | HiApprox
       def show: String =
-        val lo = if low then " (left is tightened)" else ""
-        val hi = if high then " (right is tigthened)" else ""
+        val lo = if low then " (left is approximated)" else ""
+        val hi = if high then " (right is approximated)" else ""
         lo ++ hi
   end ApproxState
   type ApproxState = ApproxState.Repr

compiler/src/dotty/tools/dotc/typer/ErrorReporting.scala

@@ -128,14 +128,14 @@ object ErrorReporting {
       val c = ctx.typerState.constraint
       val constraintText =
         if c.domainLambdas.isEmpty then
-          "empty constraint"
+          "the empty constraint"
         else
-          i"""following constraint:
+          i"""a constraint with:
              |${c.contentsToString}"""
       i"""
         |${TypeComparer.explained(_.isSubType(found, expected), header)}
         |
-        |The tests were made under the $constraintText"""
+        |The tests were made under $constraintText"""
 
     /** Format `raw` implicitNotFound or implicitAmbiguous argument, replacing
      *  all occurrences of `${X}` where `X` is in `paramNames` with the