Interpolation Theorems for L 2+ k, k. - Ruggero Ferro (J. Symb. Log., 1978)

A Theory of Sets with the Negation of the Axiom of Inflnity. - Ruggero Ferro; Stefano Baratella (Math. Log. Q., 1993)

Non Standard Regular Finite Set Theory. - Ruggero Ferro; Stefano Baratella (Math. Log. Q., 1995)