c*r
发帖数: 278 | 1
d(a,b) + d(c,d) ≤ d(a,c)+d(c,b) + d(c,b)+d(b,d) (3)
= d(a,c)+d(b,d) if d(c,b)=0 => c=b.
OR
d(a,b) + d(c,d) ≤ d(a,d)+d(d,b) + d(c,b)+d(b,d) (3)
= d(a,d)+d(b,c) if d(b,d)=d(d,b)=0 => b=d.
OR
.... a=c.
OR
.... a=d.
OR .... a=b, c=d.
=> Any two are equal. |
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