f:X→Y
f(E\F)=f(E)\f(F)⇒f is 1 to 1
I think it is not true
since let x1 x2 x3∈E ,x3 x4∈F,
and f(x1)=f( x2) it will be not true.
but my friend say by ∼q⇒∼p
f is not 1 to 1
⇒f(E\F)≠f(E)\f(F),and take
x1 x2∈X, f(x1)=f(x2)=y0
E={x1 ,x2} F={x2}
and can proof it is true
but I do not know which is true
how to proof it?
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