aima/csp.py
def prune(self, var, value, removals):
        "Rule out var=value."
        self.curr_domains[var].remove(value)
        if removals is not None: removals.append((var, value))
def prune(self, var, value, removals):
        "Rule out var=value."
        self.curr_domains[var].remove(value)
        if removals is not None: removals.append((var, value))
Rule out var=value.