public static Ident <Ident <T> > Duplicate <T>(Ident <T> ident) where T : notnull => Ident <T> .δ(ident);
public static Ident <T> Flatten <T>(Ident <Ident <T> > square) where T : notnull => Ident <T> .μ(square);
public static T Extract <T>(Ident <T> ident) where T : notnull => Ident <T> .ε(ident);
public static Ident <T> Of <T>(T value) where T : notnull => Ident <T> .η(value);