Vending Machine in NuSMV - model-checking

Question

I am new to NuSMV, I am trying to create Vending Machine implementation from Kripke structure, I have three boolean (coin, selection, brewing) as well as three states.However, When I compile the code I receive "Line 25: at token ":": syntax error" If anyone sees any errors in my code I would appreciate the help.
Kripke structure
my attempt to write the code is as follow:
MODULE main
VAR
location : {s1,s2,s3};
coin : boolean;
selection: boolean;
brweing: boolean;
ASSIGN
init(location) := s1;
init(coin) := FALSE;
init(selection) := FALSE;
init(brweing) := FALSE;
next(location) :=
case
location = s1 : s2;
TRUE: coin;
esac;
next(location) :=
case
location = (s2 : s3 & (TRUE: selection));
location = (s2 : s1 & (FALSE: selection) & (FALSE: coin));
esac;
next(location) :=
case
location = (s3 : s3 & (TRUE: brewing));
location = (s3 : s1 & (FALSE: selection) & (FALSE: coin) & (FALSE: brewing));
esac;
-- specification
• AG [s ⇒ b] whenever a selection is made coffee is brewed for sure.
• E [(¬s) U (b)] the coffee will not be brewed as no selection were made.
• EF[b] there is a state where coffee is brewed.

Answer 1

The line (among others)
location = (s2 : s3 & (TRUE: selection));
doesn't make much sense. You need only one next statement to assign the next location from all possible values of location. Also, you don't need to declare coin, selection, and brewing as variables. Use DEFINE to define their values based on location:
MODULE main
VAR
location : {s1,s2,s3};
ASSIGN
init(location) := s1;
next(location) :=
case
location = s1 : s2;
location = s2 : {s1,s3};
location = s3 : {s1,s3};
esac;
DEFINE
coin := location = s2 | location = s3;
-- similarly for selection and brewing

Answer 2

What I understand from the model is that coin, selection and brew are not only labels but events that trigger the transition. If so, I would write the model like this:
MODULE main
VAR
location: {s1, s2, s3};
coin: boolean;
selection: boolean;
brew: boolean;
abort: boolean;
INIT
!coin & !selection & !brew;
ASSIGN
init(location) := s1;
next(location) := case
location = s1 & next(coin) : s2;
location = s2 & next(selection) : s3;
location = s2 & next(abort) : s1;
location = s3 : {s1, s3};
TRUE : location;
esac;
next(brew) := (next(location) = s3);
next(coin) := case
next(state) = s1 : FALSE;
state = s1 : {TRUE, FALSE};
TRUE : coin;
esac;
next(selection) := case
state = s2 : {TRUE, FALSE};
next(state) = s1 : FALSE;
esac;