doublec(j) is TRUE <=> j,(j-1) contain a double consonant.

def doublec(self, j):
        """doublec(j) is TRUE <=> j,(j-1) contain a double consonant."""
        if j < (self.k0 + 1):
            return 0
        if self.b[j] != self.b[j - 1]:
            return 0
        return self.cons(j)