Answer

Yes, in common Jain practice, a Chhath / Attham / longer Tapasya may involve 1, 2, or 3 Upvas, and in between or before/after it, a person may do Ekashna or Biyashna / Beashna depending on strength, health, and guidance.

But strictly speaking:

• Upvas means complete fasting for the day, usually only boiled water during permitted time if one is taking water.
• Ekashna means eating one time in the day.
• Biyashna / Beashna means eating two times in the day.
• Attham traditionally means 3 continuous Upvas.

Explanation

If you are asking whether it is acceptable to do something like:

• 1 Upvas, then Ekashna, then Upvas
• 2 Upvas, then Ekashna or Biyashna
• 3 Upvas as Attham

then this can be done as a form of tapasya, but it should be called correctly according to what is actually performed.

For example:

• 3 continuous Upvas = Attham
• 2 continuous Upvas = Chhath
• 1 Upvas = Upvas
• Upvas with Ekashna in between = a mixed tapasya, not technically continuous Attham

Spiritual Understanding

In Jain Dharma, the purpose of tapasya is not only to reduce food, but to reduce:

• Attachment to taste
• Passions like anger, pride, deceit, and greed
• Carelessness in thoughts, speech, and actions

So whatever tapasya you do, it should be done with:

• Peaceful mind
• Samayik, Pratikraman, Swadhyay, or Jap
• No ego or comparison
• Care for health and capacity

Takeaway

Attham means 3 continuous Upvas. If Ekashna or Biyashna comes in between, it is still a good tapasya, but it is not called continuous Attham. It is best to follow your capacity and take guidance from your Guru Bhagwant or knowledgeable elder.