 The so @-@ called " space frame " had already been used by Alberto <unk> in the 1930s , and the two artists became friends in the 1960s . However <unk> had by 1949 used it only in <unk> contexts before <unk> 's <unk> , and in turn influenced his use in " The Cage " of 1950 . A similar two dimensional construct is found in Henry Moore 's works , notably his " <unk> for King and Queen " , constructed three years after <unk> 's Head . It is difficult to <unk> how these artists influenced and informed each other . What is notable is that <unk> continued to use the motif , with intervals until the end of his life . Sylvester suggests his finest example is the 1970 Three Studies of the Male Back . 
