COLLIER is a fortran library for the numerical evaluation of one-loop scalar and tensor integrals appearing in perturbative relativistic quantum field theory with the following features: * scalar and tensor integrals for high particle multiplicities * dimensional regularization for ultraviolet divergences * dimensional regularization for soft infrared divergences (mass regularization for abelian soft divergences is supported as well) * dimensional regularization or mass regularization for collinear mass singularities * complex internal masses (for unstable particles) fully supported (external momenta and virtualities are expected to be real) * numerically dangerous regions (small Gram or other kinematical determinants) cured by dedicated expansions * two independent implementations of all basic building blocks allow for internal cross-checks * cache system to speed up calculations

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