This removes Ralf's hack of using later_car, which is not function in the logic.

Thanks to Aleš for suggesting this.

    The idea on magic wand is to use it for curried lemmas and use ⊢ for uncurried lemmas.

Use COFEs only for the recursive domain equation solver

The old choice for ★ was a arbitrary: the precedence of the ASCII asterisk *
was fixed at a wrong level in Coq, so we had to pick another symbol. The ★ was
a random choice from a unicode chart.

The new symbol ∗ (as proposed by David Swasey) corresponds better to
conventional practise and matches the symbol we use on paper.