How to best add assumption that many variables are positive?

Question

I often need to check whether integrals are solvable in closed form and use a notebook with 5–10 variables that need to be assumed positive. Is there a better way of doing this than adding the clunky line:

$Assumptions=a>0&&b>0&&c>0&&d>0&&f>0; ?

I tried $Assumptions={a,b,c,d,f}>0; but it didn't work.

Answer 1

$Assumptions = Element[{a, b, c, d, f}, PositiveReals] ;
Simplify[Sign[a + b + c]]

 1

$Assumptions = {};
Simplify[Sign[a + b + c]]

 Sign[a + b + c] 

$Assumptions = Thread[{a, b, c, d, f} > 0] ;
Simplify[Sign[a + b + c]]

 1

$Assumptions = AllTrue[{a,b,c,d,f}, Positive] ;
Simplify[Sign[a+b+c]]

 1