= Solution
\b[<Small data global regularity for wave maps> holds in four spatial dimensions.] Smallness is measured in sufficiently high weighted <Sobolev norms> relative to a constant map, with localized compatible <Cauchy data>. The <vector field method for wave equations> gives derivative decay $(1+t)^{-3/2}$. This is time-integrable, so <commuted wave energy> estimates close a small-data <bootstrap argument> for the derivative-quadratic <semilinear wave equation>. Higher regularity persists. No smallness of energy alone is asserted.
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