NETMaths

Is this true?

d(Tx, Ty) < d(x, y) for all x ≠ y on a complete space ⇒ T has a fixed point

No — it is false.

The counterexample

T(x) = x + 1/x on

Distances strictly decrease but no contraction constant k < 1 exists; no fixed point.

The kind of mistake this is

Hypothesis dropped

A theorem applied without checking one of its preconditions.

Drill statements like this

Others that fail the same way

From Metric SpacesCompleteness and Baire category

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