# Sorry, but I'm in dire need(Proofs)

by QuantumDefect
Tags: dire, needproofs
 P: 62 Hello, I need some help. Could someone kick me(hard please) in the right direction here? Here are the statements I need to prove: 1) If g of f is injective, then f is injective 2) If g of f is subjective, then g is subjective where g and f are functions where f:A->B and g:B -> C where A,B and C are sets Any kicks in the right direction would be GREATLY appreciated. Thank you.
 P: 302 Both can be done easily by contradiction.
 HW Helper P: 2,644 Start with the definitions of injections and surjections (note the spelling of the latter), and draw functional mappings (domain/codomain diagrams). The proof is fairly easy from inspecting the mappings. Wikipedia has fairly good pages on these subjects, complete with the mappings you need for the proof : http://en.wikipedia.org/wiki/Injective_function http://en.wikipedia.org/wiki/Surjection

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