To justify reformation of instrument, mistake must be proven by clear and convincing evidence. Where there is no mistake as to identity of land intended to be conveyed, but there is a mistake in description of it, equity may reform the instrument to conform to the true intentions of the parties. In this case, the mistake was discovered when a survey was made. Booth v. Wilkinson, 195 Neb. 730, 240 N.W.2d 578 (1976); Ready Sand and Gravel Co. v. Cornett, 184 Neb. 726, 171 N.W.2d 775 (1969); Lippire v. Eckel, 178 Neb. 643, 134 N.W.2d 796 (1965).