What does class "call" mean? How do I make class "formula" into a "call"?

Hello R Users! 
I have a list called "tabs" that I would like to have the same structure as
my list "eqSystem." The two look like they have the same structure but they
are different because when I look at their attributes, class(eqSystem[[1]])
is "call" but class(tabs[[1]]) is "formula". I want to have class(tabs[[1]])
as a call too. 

So what does "call" mean? 

And how do I make an object of class "formula" be of class "call"? 
Thank you so much!!!--Rita

class(tabs)

[1] "list"

class(tabs[1])

[1] "list"

class(tabs[[1]])

[1] "formula"> class(eqSystem)
[1] "list"

class(eqSystem[1])

[1] "list"

class(eqSystem[[1]])

[1] "call"

Rita
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"If you think education is expensive, try ignorance."--Derek Bok

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