If we know the types of `a` & `b` start searching.
If we know the types of `a` & `b` start searching.

This is helpful when defining auto-implicits of the form:

    pairEqF : DecEq a
           => (thisX, x, y : a)
           -> {prfRefl : Equal x thisX}
           -> (prfEq   : decEq x thisX = Yes prfRefl)
           => Pair a a
    pairEqF thisX x y {prfRefl} {prfEq} = MkPair x y

before auto-implicit search would fail to find `Refl` for `prfRefl`.
With this fix the solution is found.

This fix means we can avoid having to write the following.

    pairEqF' : DecEq a
            => (thisX, x, y : a)
            -> (prfEq   : decEq x thisX = Yes (the (Equal x x) Refl))
            => Pair a a
    pairEqF' thisX x y {prfEq} = MkPair x y

mmhelloworld/idris-jvm,mmhelloworld/idris-jvm,mmhelloworld/idris-jvm,mmhelloworld/idris-jvm,mmhelloworld/idris-jvm,mmhelloworld/idris-jvm