Core is an extension of Core_kernel. The unmodified libraries can be found there.
module Bigbuffer = Core.Bigbuffermodule Bigstring = Core.Bigstringmodule Bigstring_marshal = Core.Bigstring_marshalmodule Caml = Core.Camlmodule Command = Core.Commandmodule Condition = Core__.Core_conditionmodule Core_stable = Core__.Stablemodule Crc = Core.Crcmodule Daemon = Core.Daemonmodule Date = Core__.Core_datemodule Filename = Core__.Core_filenamemodule Interval = Core.Intervalmodule Interval_intf = Core.Interval_intfmodule Iobuf = Core.Iobufmodule Iobuf_debug = Core.Iobuf_debugmodule Iobuf_intf = Core.Iobuf_intfmodule Linux_ext = Core.Linux_extmodule Lock_file = Core.Lock_filemodule Mac_address = Core.Mac_addressmodule Md5 = Core.Md5module Digest = Md5module Mutex = Core__.Core_mutexmodule Nano_mutex = Core.Nano_mutexmodule Piecewise_linear = Core.Piecewise_linearmodule Process_env = Core.Process_envmodule Schedule_v4_deprecated = Core.Schedule_v4_deprecatedmodule Schedule_v5 = Core.Schedule_v5module Signal = Core.Signalmodule Squeue = Core.Squeuemodule Sys = Core__.Core_sysmodule Thread = Core__.Core_threadmodule Time = Core__.Core_time_floatmodule Time_common = Core.Time_commonmodule Time_ns = Core__.Core_time_nsmodule Time_stamp_counter = Core.Time_stamp_countermodule Timing_wheel_float = Core.Timing_wheel_floatmodule Unix = Core__.Core_unixmodule User_and_group = Core.User_and_groupmodule Uuid = Core.Uuidmodule Version_util = Core.Version_utilmodule Weak_hashtbl = Core.Weak_hashtblval sec : Core_kernel__.Import.float ‑> Time.Span.t