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Description: The Euler phi function is a multiplicative function, meaning that it distributes over multiplication at relatively prime arguments. Theorem 2.5(c) in ApostolNT p. 28. (Contributed by Mario Carneiro, 24-Feb-2014)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | phimul | |- ( ( M e. NN /\ N e. NN /\ ( M gcd N ) = 1 ) -> ( phi ` ( M x. N ) ) = ( ( phi ` M ) x. ( phi ` N ) ) ) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | eqid | |- ( 0 ..^ ( M x. N ) ) = ( 0 ..^ ( M x. N ) ) |
|
| 2 | eqid | |- ( ( 0 ..^ M ) X. ( 0 ..^ N ) ) = ( ( 0 ..^ M ) X. ( 0 ..^ N ) ) |
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| 3 | eqid | |- ( x e. ( 0 ..^ ( M x. N ) ) |-> <. ( x mod M ) , ( x mod N ) >. ) = ( x e. ( 0 ..^ ( M x. N ) ) |-> <. ( x mod M ) , ( x mod N ) >. ) |
|
| 4 | id | |- ( ( M e. NN /\ N e. NN /\ ( M gcd N ) = 1 ) -> ( M e. NN /\ N e. NN /\ ( M gcd N ) = 1 ) ) |
|
| 5 | eqid | |- { y e. ( 0 ..^ M ) | ( y gcd M ) = 1 } = { y e. ( 0 ..^ M ) | ( y gcd M ) = 1 } |
|
| 6 | eqid | |- { y e. ( 0 ..^ N ) | ( y gcd N ) = 1 } = { y e. ( 0 ..^ N ) | ( y gcd N ) = 1 } |
|
| 7 | eqid | |- { y e. ( 0 ..^ ( M x. N ) ) | ( y gcd ( M x. N ) ) = 1 } = { y e. ( 0 ..^ ( M x. N ) ) | ( y gcd ( M x. N ) ) = 1 } |
|
| 8 | 1 2 3 4 5 6 7 | phimullem | |- ( ( M e. NN /\ N e. NN /\ ( M gcd N ) = 1 ) -> ( phi ` ( M x. N ) ) = ( ( phi ` M ) x. ( phi ` N ) ) ) |