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

1. ### QuantumDefect

64
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.

304
Both can be done easily by contradiction.

3. ### Curious3141

2,970
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

Last edited: May 16, 2006