Let H be a subgroup of a group G. Let ∼H and ρH be the equivalence relation in G introduced in class given by
x∼H y⇐⇒x−1y∈H, xρHy⇐⇒xy−1 ∈H.
The equivalence classes are the left and the right cosets of H in
G, respectively. Prove that the functionφ: G/∼H →G/ρH given
by
φ(xH) = Hx−1
is well-defined and bijective. This proves that the number of left and right cosets are equal.
Well-defined:
Where
Consider
So that
But
So that
And so
Meaning is well defined
For bijectivity: let
Then so
Therefore the given function is both well defined and bijective
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