a is B
a is B b

====

pattern matching:

a is PODMINKA-NA-INSTANCI

a is null

operatory na vyrazech typu bool:	&&	||	!
operatory skladajici podminky:		and	or	not

a is null
a is not null

a is B
a is not B

< 4

int x = ...

x is < 4
x < 4

neplati: x < 4
         x >= 4

!(x < 4)

x is not < 4

====

introducing nullability implicitly:
+ null-forgiving operators:

var b1 = a.Length;	// X b1 = ...
          \- X -/

var b2 = a?.Length;	// X? b2 = ...
           \- X -/  


var c1 = a[some-index-value];	// X c1 = ...
          \------- X ------/

var c2 = a?[some-index-value];	// X? c2 = ...
           \------- X ------/

record Person(string FirstName, string? LastName);
record Incident(string Info, Person? Person);

Incident i = ...
i.Person?.LastName?.Length ---> int?