https://www.cnblogs.com/yeungchie/
procedure(ycHowFar(a b) prog((xAB yAB sAB) xAB = xCoord(a) - xCoord(b) yAB = yCoord(a) - yCoord(b) sAB = sqrt(xAB ** 2 + yAB ** 2) return(sAB) ) )
ycHowFar(0:0 1:1) =>1.414214