Description: If two neighbors U and W of a vertex X have a common neighbor A in a friendship graph, then this common neighbor A must be the vertex X . (Contributed by Alexander van der Vekens, 19-Dec-2017) (Revised by AV, 2-Apr-2021) (Proof shortened by AV, 13-Feb-2022)
Ref | Expression | ||
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Hypotheses | frgrnbnb.e | |
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frgrnbnb.n | |
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Assertion | frgrnbnb | |