Make it as simple as possible, but not simpler: The Programming Language Oberon

PROCEDURE Sqrt(x: REAL): REAL; (*0 < x < 2*)

VAR y, c: REAL;

BEGIN y := x; c := 1.0 – x;

WHILE c > e DO

(*y2 = x×(1-c), c >= 0*)

y := y × (1.0 + 0.5×c);

c := c × c × (0.75 + 0.25×c)

END ;

RETURN y (*x×(1-e) <= y2 < x*)

END Sqrt