435 A.2d 289 Joseph Schaefer and Constance Schaefer, Appellants v. Zoning Board of Adjustment of the City of Pittsburgh, Appellee. Commonwealth Court of Pennsylvania.Argued May 7, 1981 October 6, 1981. Zoning — Non-conforming use — Abandonment — Variance-Unnecessary hardship — Burden of proof — Economic hardship — Knowledge of zoning status — Estoppel — Innocent […]