1. A method for identifying errors in program code, comprising: performing by a processor the steps including, counting in the program code respective numbers of observances of at least one correctness rule by different code instances that relate to the at least one correctness rule, wherein each code instance has an associated counted number of observances of the correctness rule by the code instance; counting in the program code respective numbers of violations of the at least one correctness rule by different code instances that relate to the at least one correctness rule, wherein each code instance has an associated counted number of violations of the correctness rule by the code instance; determining for each code instance a respective likelihood of validity of the code instance as a function of the counted number of observances and counted number of violations, wherein the likelihood of validity indicates a relative likelihood that a related code instance is required to observe the correctness rule; and outputting the code instances in order of the likelihood of validity of a violated correctness rule.