1. A non-transitory computer-readable recording medium storing therein a verification support program that causes a computer to execute: acquiring an implementation description of a verification target; identifying, based on the implementation description, a combination of input gates of the verification target, the input gates each receiving an input signal; detecting a pair of output cones for the combination of input gates identified at the identifying, each of the output cones including gates that are of the verification target and to which input signals from the combination of input gates reach; detecting, for the combination of input gates, a common output cone that includes gates common to the pair of output cones detected at the detecting the pair of output cones; calculating, based on the common output cone detected at the detecting the common output cone, a degree of relation between the input gates making up the combination; determining, for the combination of input gates, a first strength of relation according to a calculation result at the calculating; setting a second strength of relation for a combination of the input gates, the combination being based on a specification of the verification target and corresponding to the combination identified at the identifying; judging whether the second strength of relation set at the setting and the first strength of relation determined at the determining coincide; and outputting a result of the judging.