Prefix every variable of the user query is renamed with before rewriting, by the pipeline runner.
This is the only prefix the rewriting classifies on: a variable in a cluster carries it exactly when it
came from the user query, and every other variable in that cluster belongs to the mapping. Both
ClusterSolver.mappingVarsOf and ClusterSolver.sortClusters are defined by it, so it has to stay
disjoint from VAR_PREFIX_MAPPING and VAR_PREFIX_MERGED_HEAD - and the underscore is part
of it, a test against a bare uq also matching a user variable named ?uqx.
Prefix every variable of the user query is renamed with before rewriting, by the pipeline runner.
This is the only prefix the rewriting classifies on: a variable in a cluster carries it exactly when it came from the user query, and every other variable in that cluster belongs to the mapping. Both
ClusterSolver.mappingVarsOfandClusterSolver.sortClustersare defined by it, so it has to stay disjoint from VAR_PREFIX_MAPPING and VAR_PREFIX_MERGED_HEAD - and the underscore is part of it, a test against a bareuqalso matching a user variable named?uqx.