def mac(csp, var, value, assignment, removals):
    "Maintain arc consistency."
    return AC3(csp, [(X, var) for X in csp.neighbors[var]], removals)
def mac(csp, var, value, assignment, removals):
    "Maintain arc consistency."
    return AC3(csp, [(X, var) for X in csp.neighbors[var]], removals)
Maintain arc consistency.