英语翻译
How many functions are there from the set {1,2,3,...,n},where n is a positive integer,to the set {0,1}
a) that are one-to-one?
b) that assign 0 to both 1 and
c) that assign 1 to exactly one of the positive integers less than
主要是b和c看不懂assign to both...excactly