tsort(deps)
# [1] "std"            "ieee"           "dware"          "gtech"          "ramlib"
# [6] "std_cell_lib"   "synopsys"       "dw01"           "dw02"           "dw03"
#[11] "dw04"           "dw05"           "dw06"           "dw07"           "des_system_lib"