The IF field doesn't support AND and OR. (Have a look in Word Help for the
syntax of these fields!)
If you prefer to use AND and OR explicilty, you can use the following
approach
Use { COMPARE } to make the comparisons, e.g.
{ COMPARE a = b }
gives 1 if a = b and 0 if a <> b
then use the and and or functions within the { = } field to do the logic:
{ =and(a,b) } is 0 if a is 0 or b is 0, and 1 if a and b are 1
then wrap that inside an IF to give the result you need
{ IF { =and(a,b) } = 1 "result if both a and b are non-zero" "result if
either a or b is 0" }
e.g. to take your example,
{ IF { =or({ COMPARE { MERGEFIELD Appt_Provider } = "Provider1" },
{ COMPARE { MERGEFIELD Appt_Provider } = "Provider 2" }) } = 1 "Yes",
"No" }
(I think!)
You can nest ors and ands within the { = } field but notice that in the case
of multiple ors you can should also be able to use
{ IF { ={ COMPARE { MERGEFIELD Appt_Provider } = "Provider1" }+
{ COMPARE { MERGEFIELD Appt_Provider } = "Provider 2" } } > 0 "Yes", "No" }
Not the way I'd design the "field language" but there you go.