cvc(i) is TRUE <=> i-2,i-1,i has the form consonant - vowel - consonant
        and also if the second c is not w,x or y. this is used when trying to
        restore an e at the end of a short  e.g.

           cav(e), lov(e), hop(e), crim(e), but
           snow, box, tray.

def cvc(self, i):
        """cvc(i) is TRUE <=> i-2,i-1,i has the form consonant - vowel - consonant
        and also if the second c is not w,x or y. this is used when trying to
        restore an e at the end of a short  e.g.

           cav(e), lov(e), hop(e), crim(e), but
           snow, box, tray.
        """
        if (
            i < (self.k0 + 2)
            or not self.cons(i)
            or self.cons(i - 1)
            or not self.cons(i - 2)
        ):
            return 0
        ch = self.b[i]
        if ch == "w" or ch == "x" or ch == "y":
            return 0
        return 1