def METHOD_NAME(v0,v1,v2,element_add, coords_add, CHbond,a,b,c):
    vector1 = [v1[0] - v0[0],v1[1] - v0[1], v1[2] - v0[2]]
    vector2 = [v2[0] - v0[0],v2[1] - v0[1], v2[2] - v0[2]]
    unit_cell_fold(vector1, a,b,c)
    unit_cell_fold(vector2, a,b,c)
    norm(vector1)
    norm(vector2)
    angle = angle_2vectors(vector1, vector2)
    if(angle > 116.0):
        newvec = [vector1[0] + vector2[0],vector1[1] + vector2[1],vector1[2] + vector2[2]]
        norm(newvec)
        x = v0[0] - newvec[0] * CHbond
        y = v0[1] - newvec[1] * CHbond
        z = v0[2] - newvec[2] * CHbond
        newcoords = [x,y,z]
        element_add.append('H')
        coords_add.append(newcoords)
    else:
        print 'warning sp3 C not programed yet angle = %f'%angle
    return            