Table 1.

Symbols of quantities and parameters^(I)

I	The average relative infectivity of a virion
p	The probability that a protomer is functional
q	The probability that a trimer is functional
C,r,R,P,N	Standard symbols in combinatorial and probability analysis; the number of ways of combining r objects out of N is expressed as NCr=N!/(r!(N−r)!). P(R) is the probability of R. (This R is unrelated to the R2 that is a measure of the goodness of fits.)
n	The number of trimers per virion. For virions with mixed Env, n is the number of functional trimers plus the number trimers that are inactive because of incorporation of inert Env. Thus n does not include spontaneously inactived trimers.
S	Number of non-functional protomers that inactivate a trimer
L	Number of non-functional trimers that inactivate a virion
T	Minimum number of functional trimers a virion requires for infectivity
a	Parameter allotting weight to liminal or incremental component in a model spectrum at the level of the virion. Constrained as 0≤a≤1; the greater the value of a, the more weight given to the incremental component
c	Coefficient allotting weight to a particular threshold, i.e., a value of L in a gradual liminal model
b	Parameter given various exponents (z=[0,1,2,3]) that give optimal values to the coefficients for each respective threshold; constrained to b≥1
h	Parameter giving weight to protomeric contributions to trimer function along the spectrum from S=1 to proportionally incremental effects of protomers, 0≤h≤1; the greater the value of h, the more weight given to the incremental protomeric component

^(I)Since the current modeling is more comprehensive and complex than that in (Herrera et al., 2006), and in order to maximize consistency with the rest of the literature, some of these symbols differ from those in that reference or signify quantities that are not found there.