a. Make a circle with A partial arc with a center arbitrary radius R is cut off the legs of angle AB and conditioned on n and m
b. Create an arc from the A1 well of radius R1 (R = R1) that cut the legs angle in m1 C1 A1
c. Create an arc from a point m with radius r = nm
d. Create also arc of radius r1 = r from the point m1 this arc cuts the first arc (radius R1) at point n
e. Pull the line A1 n1 which is the leg angle A1 B1 A1 B1 C1 then angle = angle BAC
