A module internal to Incremental. Users should see Incremental_intf.

A `Snapshot.t` is a kind of DAG node.

`include module type of sig ... end`
`type 'a t``= 'a Incremental_kernel__Types.Snapshot.t``=` `{`

`main : 'a Incremental_kernel__Types.Node.t;`
`at : Incremental_kernel__.Import.Time_ns.t;`
`before : 'a;`
`value_at : 'a Incremental_kernel__Types.Node.t;`

`}```
`include Core_kernel.Invariant.S1 with type a t := a t`
`type 'a t`````
`val invariant : 'a Base__.Invariant_intf.inv ‑> 'a t Base__.Invariant_intf.inv`
`include Incremental_kernel__.Sexp_of.S1 with type a t := a t`
`type 'a t`````
`include sig ... end`
`val sexp_of_t : ('a ‑> Base.Sexp.t) ‑> 'a t ‑> Base.Sexp.t`